1. Field of the Invention
The present invention relates to an ion-exchanger comprising zirconium hydroxide supported on active carbon, which is useful for application fields utilizing ion exchange or ion adsorption such as separation, removal, recovery, purification, and concentration of specific ions in an aqueous solution or in an organic solvent, and removal of noxious ions from waste water. The present invention relates also to a process for producing the ion-exchanger, and process for removing a multiply charged ions employing the ion-exchanger.
2. Description of the Related Art
Ion-exchange resins are widely used as ion-exchangers. However, the ion-exchange resin is limited in the application fields thereof owing to poor resistance to radiation and heat, and poor ion selectivity in a solution containing many kinds of salts or high concentration of electrolyte.
Inorganic ion-exchangers, on the other hand, have excellent properties such as high radiation resistance, high heat stability at high temperature, and high ion selectivity, and are promising in application fields of water treatment at a high temperature, concentration and purification of a substance, and so forth. In particular, an inorganic ion-exchanger comprising zirconium hydroxide having amphoteric ion exchangeability has low solubility in water and high selectivity to specific ions, being suitable for removal and recovery of noxious substances, impurities, and the like.
However , the zirconium hydroxide having the amphoteric ion exchangeability, which is usually produced from a halide, oxyhalide, or a mineral acid salt of zirconium by contact with an alkali, is in a form of a gel or a coagulate and is difficult in industrial handling.
JP-A-60-44056, for example, discloses a process for treating a salt solution by a fixed-bed packed column system employing zirconium hydroxide supported on a cation-exchange resin having sulfonic acid functionality. In this process, although sulfate ions are selectively adsorbed and removed by zirconium hydroxide on the ion-exchange resin, the efficiency of regeneration by desorption is low, and a large amount of expensive cation-exchange resin is required for supporting the zirconium hydroxide which is uneconomic JP-A-60-168541 discloses use of a crosslinking or noncrosslinking curable organic fluoroplastic as the binder. JP-A-3-131349 and JP-A-4-45854 disclose processes employing a clay mineral and a metal alkoxide or a hydrosol as the binder. These processes have disadvantages of limitation in preparation conditions and troublesomeness in operation. When the mechanical strength of the particles is raised, the ion exchange properties such as the ion exchange capacity and the ion exchange velocity are lowered in comparison with the ones in a powdery state.
JP-A-3-153522 discloses a process for treatment of a salt solution with dry powdery zirconium hydroxide. This process employs a simple zirconium hydroxide in a slurry state as an ion-excahger. This process involves the problem that the ion-exchanger is liable to be pulverized or crushed by a stirrer or a pump to leak out of the system, or the load of a filter machine is liable to become larger. In use of an inorganic ion-exchanger in a packed column system, the fine powdery inorganic ion-exchanger should be molded into a suitable shape and size by use of a binder. However, the binders tend to be dissolved out in acidic or alkaline conditions, which limits the application fields of the ion-exchanger.